As adults they are black. The chicks of the Turkey vulture are white though. (The chicks of the Black vulture are more dark beige.)

Life is their enemy, death is their friend

They are scavengers, eating from dead animals. As long as these animals are still alive they have nothing to eat, but as soon as the animals die they'll have plenty to eat.

One never speaking, one never silent

Not sure about the first part, since the adults also make sounds. But the "one never silent" could be for the chick begging for food. As all birds, chicks begging for food try to make as much noise as possible to alert the parents.

A black hole and a white hole.
The white hole is theoretically the daughter of a black hole.
Nothing can live around them.
A black hole absorbs everything, a white hole does not absorb anything.
The destiny of all black holes may be a white hole.